Loren said it straight up “Chairs are hard”, especially as a “one-off”.Before using that prized walnut build a couple for the front porch out of more forgiving wood.There are a number of Windsor chair making classes out there.I’d also avoid mixing air, kiln or green wood. And if you do mix species I’d also be mindful of wood movement trying to use similar spec’d choices.I’ve seen but haven’t used thermally treated lumber – could be an interesting option.